Mersenne Twister Seed

[chonJi]

Oh man, can anybody help me get a working version of the mersenne twister going? i have tried about three or four different implementations now, including direct c++ ports of the original C and versions in C all kinds, i can run all the samples supplied with these implementations and see lots of stacks of floating point numbers, but i CANNOT get any of them to do what you want, ie give me a whole number from range n to n and SEED the blasted thing so i get different output each time!

I tried the seed by array, seed with 0, seed with bloody sunflower seeds, i just get same output every time.

Can somebody describe how to use the major seed functions that you see with the Mersenne twister?

Cheers all.

[Athar]

You can just initialize the array with a simple lcg algo or something similar, which you seed with the seed intended for the mersenne twister.
You generate a number in a certain range with mersenne_rand()%(max-min+1)+min;

[chonJi]

So something like this example to generate a seed value:

#include <stdio.h>
 
 #define M 2147483647
 #define A 16807
 #define Q ( M / A )
 #define R ( M % A )
 
 static int seed = 1;
 
int jsw_rand ( void )
{
  seed = A * ( seed % Q ) - R * ( seed / Q );

  if ( seed <= 0 )
    seed += M;

  return seed;
}

int main ( void )
{
  int i;

  for ( i = 0; i < 10; i++ )
    printf ( "%d ", jsw_rand() );
  printf ( "...\n" );

  return 0;
}

Then i put this into my chosen function from the mersenne twister..

How do i get a common garden variety integer returned?, casting? the only thing these functions seem to deal in is long unsigned ints and what have you

EDIT: The value returned from this function is the same every time, so how is that of any use?

[chonJi]

Heres a version i tried, same output every time. although i now have the range sorted, thanks.

#include<stdlib.h>
#include <cstdio>
#include "mtrand.h"

#define M 2147483647
#define A 16807
#define Q ( M / A )
#define R ( M % A )

static int seed = 1;

int jsw_rand ( void )
{
  seed = A * ( seed % Q ) - R * ( seed / Q );

  if ( seed <= 0 )
    seed += M;

  return seed;
}


int main()
{
    unsigned long temp = 0;
    int seed = jsw_rand();
    int max = 20;
    int min = 0;

    printf("SEED %d\n", seed);


    MTRand_int32 rand_num;
    rand_num.seed(seed);

    for (int i = 0; i < 10; ++i)
    {
        temp = rand_num()%(max - min+1) + min;

        printf("%1lu ", temp);
        if ((i % 5) == 4) std::printf("\n");
    }

  return 0;
}

[Athar]

Do not use #define where not necessary.
If you're using the same seed every time, you'll obviously get the same number sequence each time.
Use something that constantly changes as a seed, i.e. time(0).